1. Field of the Invention
This invention relates to a grease compatible, cured, cross-linked, mineral oil extended polyurethane which is non-spewing, a process for reclaiming or sealing electrical devices by using the mineral oil extended polyurethane and the reclaimed or sealed electrical devices formed by such process.
2. Description of the Prior Art
It is an established practice in the art to use a variety of materials to extend polymers. The extension material or extender is generally selected depending upon the desired utility of the extended polymer, such utilities including the preparation of adhesives, molded articles, construction material, flooring and a multitude of other products.
It is also known in the art to use extended polyurethanes in the preparation of these products. One development in this field is an aromatic oil extended polyurethane. The aromatic oil extended polyurethane is particularly useful in the reclamation or rehabilitation of insulated electrical devices, such as underground multi-conductor telephone cables, which have been penetrated with fluid contaminants such as water. Compared to former techniques of reclaiming such insulated electrical devices, involving the injection of acetone or an inert gas, the use of aromatic oil extended polyurethane is a considerable improvement since it remains in the electrical device, after curing in situ, and forms a hydrophobic barrier against further water and aqueous penetration.
In an analogous utility, the aromatic oil extended polyurethane may be used as an encapsulant in sealing sections of cable wherein splicing or other repairs have been performed. In this embodiment, the extended polyurethane is maintained in the vicinity of the splice and serves, not to displace fluid contaminants, but to prevent their penetration when the cable is replaced in its original position.
In either the reclamation or encapsulant utilities, a principal disadvantage of using an aromatic oil extended polyurethane in an insulated cable is that the aromatic oil tends to chemically attack the plastic (e.g., polycarbonate) conductor connectors and/or polyolefin sheathing which is typically present in the cable. Additionally, the aromatic oil poses considerable danger to installing personnel due to its toxic, volatile nature.
In an effort to overcome the aforementioned problems attendant with the use of aromatic oils, the prior art attempted to extend polyurethanes using mineral oils. These prior art systems were not entirely successful since the mineral oil tended to exude or "spew" from the mineral oil extended polyurethane, particularly at higher extensions, e.g., above about 2:1, oil to polymer. It has also been found that extended periods of time and colder temperatures cause this "spewing" phenomenon, even at lower extensions.
The problems of the prior art were solved or substantially reduced by the mineral oil extended polyurethane described and claimed in applicant's U.S. Pat. No. 4,008,197. As more fully discussed therein, a non-spewing, cured, cross-linked, mineral oil extended polyurethane is obtained via the use of a defined polyurethane and a defined coupling agent.
The non-spewing, cured, cross-linked, mineral oil extended polyurethane of applicants' patent is particularly useful in the reclamation or encapsulation of underground cables in that it possesses excellent chemical and electrical properties. Specifically, this mineral oil extended polyurethane does not spew oil, even with oil extensions as high as about 10:1, to oil polymer, or over extended periods of time and at colder temperatures, and does not present a health hazard to installing personnel. The mineral oil extended polyurethane also does not chemically attack the plastic materials normally found in underground cables. Additionally, it possesses a high insulation resistance, a high volume resistivity, a low dissipation factor and a low dielectric constant which is required in an underground cable and is relatively low in specific gravity whereby it does not greatly increase the weight of the reclaimed or encapsulated cable.
It has now been discovered that when the non-spewing, cured, cross-linked, mineral oil extended polyurethane described in applicants' patent is brought into contact with grease, which is often present in newer insulated electrical devices such as underground cables, the mineral oil tends to migrate towards the grease. The migration causes the formation of an oily film at the grease interface and tends to decrease the effectiveness of the mineral oil extended polyurethane in the prevention of aqueous contamination of the electrical device.